In this resubmission, the applicants propose to use their previously developed fibrin-specific 99mTc small tetrameric molecule agent (99mTc-F4A) to quantify and characterize thrombus formation in left ventricular assist device (LVAD) circuits and compare the nuclear signal with pump histopathology results. The panel agreed that the applicants did a good job of responding to the concerns of the previous reviewers, including eliminating the aim regarding developing a handheld device. The ability to detect thrombus formation in VAD is an unmet clinical need with high significance, the team of investigators was considered very strong and the research environment was considered good. The tetrameric probe was considered novel, with decreased plasma interference and improved affinity over previous probes. The approach was logical within the aims, although the panel was concerned that the order of Aims seemed backwards (imaging the VAD in Aim 1 and optimizing the probe in Aim 2). It was also not clear if uptake would be detectable, especially in the presence of an attenuating medium. Reviewers also expressed concern regarding lack of access to a scanner for large animal work, because they agreed that imaging in a large animal model was needed. Although these concerns tempered the enthusiasm of the reviewers for this application, the significance was thought to outweigh the difficulties, and the panel concluded that the proposed work could have a high impact on early recognition of thrombus formation in LVADs.